Aerofoil with gas discharge

ABSTRACT

Upper surface ( 13 ) of an aerofoil (or rotor blade) is provided with nozzles or slots ( 14, 16 ) at leading portion ( 15 ) and trailing portion ( 17 ) to assist attachment of airflow by discharging gas towards trailing edge ( 11 ). Gas discharged may be heated, eg coming from rocket-type combustion chambers within the aerofoil. The aerofoil may be adjustable between high profile (as shown) and low profile (for supersonic flight) using jacks that pivot sections of upper surface ( 13 ) at leading and trailing edges ( 10 - 11 ).

FIELD OF THE INVENTION

[0001] This invention relates to a high lift aerofoil with improved liftand drag characteristics, in particular but not solely to aerofoils forrotors in vertical takeoff and landing (VTOL) and short takeoff andlanding (STOL) aircraft, and to aerofoils which may be used as wings foraircraft.

[0002] It is the result of an investigation into vorticity, involvingtrapped vortexes, vortex generators and finally a bound vortexsituation.

BACKGROUND

[0003] The airflow around an aerofoil having a sharp leading edge tendsto separate at the leading edge and breakaway over the upper aerofoilsurface, depending on angle of attack. Various means have been used toreattach airflow over these aerofoils, and reduce the breakaway flowswhich generally decrease lift and increase drag.

[0004] It is an object of the present invention to provide an aerofoilwith enhanced attachment of airflow for rotors such as for VTOLaircraft, or for use on other types of aircraft wings, such as for STOL,supersonic or hypersonic type aircraft, or to at least provide thepublic with a useful choice.

SUMMARY OF THE INVENTION

[0005] In accordance with a first aspect of the present invention thereis provided an aerofoil having upper and lower surfaces, leading andtrailing edges, and least one opening provided along a leading portionof the upper surface to discharge gas away from the leading edge andassist attachment of airflow over the upper surface.

[0006] The opening may be in the form of a slot, or a series oflongitudinally aligned apertures or nozzles. In a preferred form of theinvention, there is a series of spaced apertures or nozzles arrangedlinearly along the leading portion of the upper surface.

[0007] Preferably, an opening in the form of a slot or a series ofspaced apertures or nozzles is also provided along a region of the uppersurface between the first mentioned opening(s) and a trailing surfaceportion of the upper surface, to discharge gas towards the trailing edgeand further assist the attachment of airflow over the upper surface. Thegas may be heated, perhaps by means to heat the gas, which may be acombustion chamber within the aerofoil itself, or adjacent to theaerofoil but in operable connection with the aerofoil.

[0008] The apertures or nozzles are preferably arranged to disperse thegas over the surface of the aerofoil. The apertures or nozzles mayinclude substantially V-shaped notches in their side walls.Alternatively, the width of the outlet of each nozzle or aperture may begreater than its height.

[0009] The aerofoil may be part of a rotor, or may be a wing.

[0010] In accordance with a second aspect of the present invention,there is provided a rotor assembly including: a central support; a rotorincluding a plurality of radially oriented aerofoils distributedcircumferentially around the central support; and gas supply means whichcarries pressurised gas from the central support to the aerofoils; atleast a majority of the aerofoils having a leading edge, a leading uppersurface portion, and at least one opening extending outwards along theleading upper surface portion to discharge gas from the supply meansover the upper surface away from the leading edge.

[0011] The opening may be in the form of a slot, or a series of spacedapertures or nozzles may be provided. The spaced apertures may belinearly arranged along the leading portion of the upper surface.

[0012] Each of the aerofoils is preferably inclined to oncoming airflowat an angle of about 22° or more, depending on the size of the aerofoil.A larger aerofoil may be inclined at a greater angle.

[0013] Inlet guide vanes may be arranged about the periphery of therotor to direct oncoming airflow to the aerofoils. The guide vanes arepreferably arranged at an angle to a radius of the rotor and arearranged to extend outwardly defining a direction of rotation of therotor. Each guide vane preferably extends at an angle of about 53° tothe radius of the rotor, from the central axis of the rotor to intersectwith an inner edge of the associated guide vane. Each guide vane mayalso be oriented at an angle to the axis of rotation of the rotor.Preferably, each guide vane is oriented at an angle of about 45° to theaxis of rotation of the rotor.

[0014] Preferably a ceiling is provided over the guide vanes which isadapted to cause the airflow to enter through the guide vanes.

[0015] At least a majority of the aerofoils may include at least onefurther opening a long a region of the upper surface between theopening(s) along the leading portion of the upper surface and a trailingportion of the upper surface, to discharge gas towards the trailingedge.

[0016] In accordance with a third aspect of the present invention, thereis provided an aerofoil having upper and lower surfaces, and leading andtrailing edges, at least one opening provided along a leading portion ofthe upper surface to discharge gas away from the leading edge and assistattachment of airflow over the upper surface, the aerofoil beingadjustable between a high profile configuration and a low profileconfiguration.

[0017] The opening may be in the form of a slot, or the openings maycomprise a series of apertures or nozzles spaced along the leadingportion of the upper surface. The plurality of apertures or nozzles ispreferably arranged linearly.

[0018] Preferably, the apertures or nozzles are arranged to disperse thegas over the surface of the aerofoil. The apertures or nozzles mayinclude substantially V-shaped apertures in their side walls. The widthof the outlet of each nozzle or aperture may be greater than its height.

[0019] The upper surface is preferably constituted by a leading surfaceportion. Preferably, the upper leading surface portion is constituted byan upper leading panel and the upper trailing surface portion isconstituted by an upper trailing panel.

[0020] The upper trailing panel may be detachably joined to theremainder of the upper surface to facilitate movement between the highprofile configuration and the low profile configuration. The detachablejoint is preferably in the form of a sliding lap joint. The sliding lapjoint suitably includes a roller rotatably mounted to the upper trailingpanel which is slidable in a curved channel extending from the upperleading panel.

[0021] The lower surface is preferably defined by a leading panel, acentral panel, and a trailing panel. The lower leading panel and thelower trailing panel may be hingedly connected to the lower centralpanel. The lower central panel preferably includes a transverse bendwhich defines a lower central panel leading portion and a lower centralpanel trailing portion. In a preferred embodiment, the upper leadingpanel is fixedly attached to the lower leading panel at the leadingedge, and the upper trailing panel is fixedly attached to the lowertrailing panel at the trailing edge. The lengths of the lower leadingpanel and the lower trailing panel may be significantly less than thelength of the lower central panel.

[0022] The aerofoil preferably includes two internal hydraulic jacksextending from adjacent to the lower surface to adjacent the uppersurface to facilitate adjustment between the low profile configurationand the high profile configuration. The aerofoil may include two mainstructural supporting beams. A hydraulic jack may extend between eachstructural supporting beam and a respective upper panel of the aerofoil.

[0023] The leading edge of the aerofoil is preferably rounded. Therounded leading edge may include a section through which cooling fluidor gas may pass to cool the leading edge. The section may be in the formof a pipe. The portion of the aerofoil adjacent to and including theleading edge may include a high temperature resistant layer. The hightemperature resistant layer suitably comprises a ceramic material.

[0024] The aerofoil preferably includes means to heat the gas, which maycomprise a combustion chamber within the aerofoil. A rocket chamber maybe provided within the aerofoil which is arranged to exhaust heated gasto the opening(s). Preferably, the openings comprise a plurality ofnozzles, and an arrangement is provided to exhaust heated gas from therocket chamber to at least some of the plurality of nozzles.Alternatively, one or more rocket chambers may be provided with eachopening comprising part of a respective rocket chamber.

[0025] The means to heat the gas may be provided adjacent to, but inoperable connection with, the aerofoil.

[0026] At least one further opening may be provided along a region ofthe upper surface between the opening(s) along the leading portion ofthe upper surface and a trailing surface portion of the upper surface,to discharge gas towards the trailing edge and further assist theattachment of airflow over the upper surface.

[0027] Preferably, the opening in the trailing surface portion is in theform of a slot. Alternatively, the openings in the trailing surfaceportion comprise a plurality of apertures or nozzles arranged along thetrailing surface portion of the upper surface. The plurality ofapertures or nozzles is preferably arranged linearly.

[0028] Preferably the apertures or nozzles in the trailing surfaceportion are arranged to disperse the gas over the trailing surfaceportion of the aerofoil. The apertures or nozzles in the trailingsurface portion may include substantially V-shaped apertures in theirside walls. The width of the outlet of each aperture or nozzle in thetrailing surface portion may be greater than its height.

[0029] The aerofoil is preferably a wing. In a preferred embodiment, theaerofoil is movably attached to an aircraft so that its angle ofincidence to oncoming airflow is selectively variable.

[0030] The invention may also broadly be said to consist in anyalternative combination of parts or features here referred to or shownin the accompanying drawings. Known equivalents of these parts orfeatures not expressly set out are nevertheless to be included.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order that the invention may be more fully understood, anexample will be described with reference to the accompanying drawings ofwhich:

[0032]FIG. 1 shows an aerofoil according to a preferred embodiment ofthe invention in simplified cross-section;

[0033]FIG. 2 shows a rotor according to a preferred embodiment of theinvention in simplified elevational cross-section;

[0034]FIG. 3 is a partial plan view of the rotor of FIG. 2 along line3-3;

[0035]FIG. 4 illustrates the flow over the aerofoil of a preferredembodiment of the invention in a test situation;

[0036]FIG. 5 shows a simplified cross-section of an aerofoil accordingto an alternative embodiment of the invention, the aerofoil being in ahigh profile configuration;

[0037]FIG. 6 shows the aerofoil of FIG. 5 in a low profileconfiguration;

[0038]FIG. 7 shows a simplified cross-section of an aerofoil similar tothat shown in FIG. 5, but with a rounded leading edge;

[0039]FIG. 8 shows (a) an end view, (b) a sectional plan view, and (c) asectional side view of a preferred Coanda blowing nozzle arrangement;

[0040]FIG. 9 shows a schematic sectional elevation view of a preferredcombustion chamber which may be attached to the Coanda blowing nozzlearrangement of FIG. 8;

[0041]FIG. 10 shows a schematic sectional elevation view of analternative combustion chamber, in which each chamber provides a blowingnozzle; and

[0042]FIG. 11 shows a schematic end view of a nozzle of the combustionchamber of FIG. 10.

DETAILED DESCRIPTION OF PREFERRED FORMS

[0043] An aerofoil having gas discharge slots according to the inventionhas been found to provide a marked increase in lift and forward thrust.The gas is typically heated and/or compressed air, but other gases undera range of conditions may also be used.

[0044]FIG. 1 shows a prototype aerofoil in simplified cross-section orprofile. Externally the aerofoil has sharp leading and trailing edges10, 11 and lower and upper surfaces 12, 13 respectively. A gas dischargeslot 14 lies along the aerofoil, approximately perpendicular to theprofile, in a leading portion 15 of the upper surface 13. Another slot16 lies rearwardly of the slot 14 beyond a curved portion of the uppersurface in a region between the leading portion and a trailing portion17, at or near a position of maximum thickness of the aerofoil. Mostinternal details have been omitted for clarity except chambers 18, eachof which may be a single large chamber, through which gas reaches theslots. It will be appreciated that the discharge pressure from each slotwill be determined by the flow rate (measured for example in units CFM)of gas into the respective chamber 18 as well as the geometry of thedischarge slots.

[0045] Arrow A in FIG. 1 indicates a typical direction of airflowtowards the aerofoil in use.

[0046] Arrow B indicates the leading edge breakaway flow. This is mainlydue to pressure differences and the conservation of angular momentum.The flow from just underneath the leading edge 10 increases in pressureand flows back around the leading edge, giving a powerful leading edgebreakaway flow.

[0047] Arrows C and D indicate gas blown from the slots. This blowingcreates a Coanda flow which reattaches the leading edge breakaway flowto the aerofoil.

[0048] A feature of this aerofoil is to take advantage of the power ofthe leading edge breakaway flow. The actual aerodynamic mechanisminvolved is complex.

[0049]FIG. 2 is a simplified vertical cross-section through a rotorassembly 40 for a VTOL aircraft. The rotor includes aerofoils accordingto the invention, such as those shown in FIG. 1. The rotor 20 is mountedon a central support 21 through bearings 22. Aerofoils 23 are shownmounted within a single duct 24 around the circumference of the rotor.Pressurised hot air is supplied to a manifold on the rotor through fixedducts 26 on the support and from there to individual aerofoils throughtubes 27, which rotate with the aerofoils 23 on the bearings 22.

[0050] An auxiliary engine may be provided to supply the compressed air.Alternatively, the area containing tubes 27 could also contain an aircompressor, driven by the main engines. The tubes 27 could be replacedwith a combustion zone. Alternatively the tubes 27 may carry rocketfuel, such as kerosene and hydrogen peroxide, with combustion takingplace in the chambers 18, or within the aerofoil and adjoining chambers18.

[0051]FIG. 3 is a simplified plan view of the rotor along line 3-3 ofFIG. 2, showing the aerofoils 23 oriented approximately radially forclockwise rotation overall. Again the aerofoils are shown only inoutline with areas of overlap indicated by dashed lines on theirtrailing edges. Each is inclined to its oncoming airflow atapproximately 22° as shown in FIG. 1. An optimum angle of about 26° hasbeen determined for a small size of aerofoil. Angles of greater thanabout 22° are suitable, with higher angles being particularly suitablefor larger aerofoils. The radius of the curved portion of the uppersurface of the aerofoil determines the angle of incidence to oncomingair at which the aerofoil will stall (at a given air velocity). Theangle of incidence of a larger aerofoil having a larger radius ofcurvature may be greater without stalling. Forward or backward sweepingaerofoils are also a possibility, as has been determined from testscarried out.

[0052] As shown in FIGS. 2 and 3, the rotor assembly 40 also includesfixed inlet guide vanes 42.

[0053] The inlet guide vanes 42 are spaced about the periphery of therotor assembly 40 as can be most clearly seen from FIG. 3. The guidevanes 42 are arranged at an angle of about 53° to a radius of the rotorextending from the central axis of the rotor to intersect with the inneredge 45 of the associated guide vane 42. From the inner edge 45 to theouter edge, the guide vanes 42 are arranged to extend outwardly in thesame direction as the rotation of the rotor, in this case clockwise.Although not shown, each guide vane 42 could also extend at an angle tothe axis of rotation of the. rotor, more preferably at about 45°, toprovide additional lift.

[0054] The arrangement illustrated in FIG. 2 includes a ceiling 47,which is fixed to the ducts 26 and guide vanes 42. Arrows F, G and Hillustrate the direction of the air flow through the rotor 20. Theceiling 47 causes the airflow to enter through the inlet guide vanes 42forming a vortex flow in the opposite direction to the direction ofrotation of the rotor, increasing lift.

[0055] The upper portion of the rotor assembly 40 including the support21, ducts 26, ceiling 47 and inlet guide vanes 42 are stationary. Thelower portion of the rotor assembly 40 including the rotor 20, tubes 27,duct 24 and aerofoils 23 rotate about the bearings 22 on the support 21.

[0056] The results from a rotating test rig made in accordance with theembodiment of FIGS. 2 and 3 show a coefficient of lift of up to 8 forvarious useful aerofoil velocities.

[0057] Tests have shown a favourable hovercraft ground effect can existunder the rotors giving up to 50% more lift.

[0058] A range of small scale aerofoils have been tested according tothe shape of FIG. 1. Good results were obtained for a model about 15 cmin chord length (i.e. length from leading edge to trailing edge) wherethe leading and trailing edges were formed with internal angles ofapproximately 50° and 30° respectively. The distance from the leadingedge to the first slot 14 was about one third the chord length of theaerofoil while a curved surface between the slots had a radius of aboutone quarter this chord length. Slightly concave lower surfaces anddifferent blowing slot widths and arrangements are possible. Wind tunneltests have also shown that as the chord length is increased, aproportional increase in lift may be obtained without requiring anincrease in flow rate of compressed gas into the chambers 18.

[0059] The nature of the molecular interaction between the breakawayflow B which separates from the leading edge of an aerofoil and the airor gas C which is blown out of the leading slot is not entirely clear.Air or gas from the discharge slot follows the curved upper surface 13quite closely according to the Coanda effect. A part of the breakawayflow is entrained to reduce pressure over the leading portion of theupper surface with a consequent increase in lift and forward thrust. Thetrailing slot has a similar effect, of flow reattachment and increasedlift. As the gas passes through the aerofoils it also drives themforward.

[0060] Overall the gas discharge slots are believed to have a threefoldeffect. Reattachment of the airflow increases lift and forward thrust oneach aerofoil, while jet reaction from the discharged air or gas assiststo propel them. To prevent blowing blockage through the narrow dischargeslots, they can be replaced with spaced nozzles of say about {fraction(3/16)}″ (4.76 mm) to about {fraction (5/16)}″ (8 mm) diameter. Thenozzles may have substantially V-shaped notches in their walls as willbe described below. The geometry of the aerofoil allows for a stronglightweight structure, as is required. This should provide a substantialencouragement to further development of VTOL and STOL aircraft.

[0061]FIG. 4 illustrates the flow over the aerofoil in a test situation.The test was performed by the use of an aerofoil segment having thecross-section as illustrated in the figure. The segment is fixed betweentwo plates at either end of the segment. The plates extend parallel tothe cross-section of the aerofoil segment. Air is forced to flow out ofa nozzle over the aerofoil segment. With the use of paint and oilprovided on one of the end plates, the flow over the aerofoil segmentproduces the flow pattern illustrated in the figure.

[0062]FIGS. 5 and 6 show schematically an alternative aerofoil which isadjustable between a high profile configuration and a low profileconfiguration. Many of the parts illustrated in FIGS. 5 and 6 may befound in the earlier figures, and like reference numerals are used torepresent like parts.

[0063] It will be noted that only a single Coanda blowing slot 14′ isutilised in this adjustable profile aerofoil. The position of thisCoanda blowing slot 14′ is between the two blowing slots 14, 16 shown inthe aerofoil of FIG. 1. However, one or two Coanda blowing slots may beused, depending on the performance required. The aerofoil may have twoslots arranged in a similar manner to the aerofoil in FIG. 1.

[0064] The upper surface 13 of the aerofoil shown in FIGS. 5 and 6 isconstituted by a leading surface portion and a trailing surface portionwhich are defined by an upper leading panel 15 and an upper trailingpanel 17 respectively. The lower surface 12 is constituted by a lowerleading panel 60, a lower central panel 61, and a lower trailing panel62. The lower leading panel 60 is connected to the lower central panel61 via a hinge 63, and the lower trailing panel 62 is connected to thelower central panel 61 via a hinge 64. The hinges 63, 64 are locatedtowards the leading edge 10 and the trailing edge 11 respectively, sothat the lengths of the lower leading panel and lower trailing panel aresignificantly less than the length of the lower central panel. The lowercentral panel 61 includes a transverse bend 65 which defines a lowercentral panel leading portion 66 and a lower central panel trailingportion 67.

[0065] The upper leading panel 15 and lower leading panel 60 are fixedlyattached at the leading edge 10, and the upper trailing panel 17 andlower trailing panel 62 are fixedly attached at the trailing edge 11.The upper leading panel 15 includes the gas discharge slot 14′. Theupper trailing panel 17 is detachably attached to the remainder of theupper surface via a sliding lap joint 68 positioned rearwardly of thegas discharge slot 14′. The sliding lap joint 68 includes a roller 69rotatably mounted to the upper trailing panel 17 which slidably moves ina curved channel 70 which extends rearwardly from adjacent to the gasdischarge slot 14′. Alternatively the sliding movement of the lap joint68 could be provided by means other than the roller in the curvedchannel if desired.

[0066] The aerofoil includes a pair of supports 71, 72 which are themain supporting beams for structurally connecting the aerofoil to anaircraft. The supports 71, 72 are attached to the inner surfaces of thelower central panel leading portion 66 and the lower central paneltrailing portion 67 respectively. The aerofoil includes a hydraulic jack73 pivotally connected to the inside of the upper leading panel 15 andthe support 71. A further hydraulic jack 74 is pivotally connected tothe inside of the upper trailing panel 17 and the support 72. Thesejacks serve to move the respective leading panels and trailing panelsabout the hinges 63, 64.

[0067] The aerofoil additionally includes lower profile supports 75, 76which are located between the supports 71, 72 and the leading andtrailing edges 10, 11 respectively.

[0068] When the aerofoil is to be adjusted from the high profileconfiguration shown in FIG. 5 to the low profile configuration shown inFIG. 6, the front hydraulic jack 73 is actuated to move the upperleading panel 15 downwards toward the lower central panel 61. Therearward hydraulic jack 74 is actuated concurrently to cause the uppertrailing panel 17 to move downwards toward the lower central panel 61.The movement of the roller 69 in the curved channel 70 results in asuitable wing configuration being retained throughout the movement.

[0069] When the aerofoil is in the low profile configuration shown inFIG. 6, the lower leading panel 60 is aligned with the lower centralpanel leading portion 66, and the lower trailing panel 62 is alignedwith the lower central panel trailing portion 67. Further, in the lowprofile configuration, the curved channel 67 is located inside theaerofoil between the upper trailing panel 17 and the lower central panel61.

[0070] This form of aerofoil is suitable for use as an aircraft wing.The high profile configuration shown in FIG. 5 is suitable as a highlift subsonic aerofoil wing needed for taking off and landing. Once thespeed of the aircraft increases, the wing can then close down in to thelow profile configuration shown in FIG. 6. This configuration issuitable for supersonic or hypersonic flight, for example in a STOLhypersonic airliner or space relaunch vehicle. The aerofoil may bemovably attached to an aircraft so that its overall angle of incidenceto oncoming airflow is selectively variable. This may be achieved bymovably mounting the main supports 71, 72 to an aircraft.

[0071] The gas need only be discharged through the slot 14′ for a shortperiod of time (generally in the order of about 7 seconds), as the takeoff time for a supersonic or hypersonic aircraft is very brief. Once theaircraft has accelerated along the runway, the gas can be dischargedthrough the vent or slot 14′ to produce a Coanda flow. This providesgood lift properties to aid in the take off of the aircraft. The gaswould only be applied for a few seconds until the aircraft had furtheraccelerated. Once a speed approaching supersonic has been reached, theaerofoil would be adjusted into the low profile configuration as shownin FIG. 6.

[0072] The aerofoil shown in FIG. 7 is similar to the aerofoil shown inFIGS. 5 and 6, and like reference numerals are used to indicate likeparts. The details of this aerofoil adjacent the leading edge 10 differfrom the aerofoil of FIGS. 5 and 6. The front end 10′ includes a roundedportion 101 made of a ceramic or other high temperature resistantmaterial. This high temperature resistant material extends back alongthe upper and lower leading panels a predetermined distance from theleading edge 10′ of aerofoil. The curved portion 101 includes a sectionthrough which cooling fluid such as gas or helium may pass to cool theleading edge of the aerofoil. The section is preferably in the form of apipe 103.

[0073] This form of aerofoil is again suitable for use as an aircraftwing, and more particularly for use as a wing of a space relaunchvehicle. Such vehicles must reach speeds of approximately seven timesthe speed of sound to get into orbit, and at such speeds the leadingedge of the aerofoil is exposed to very high temperatures. Hightemperatures are also encountered during re-entry into the atmosphere.The curved front edge lowers stress concentrations in the leading edgeof the aerofoil, and also enables cooling fluid or gas to be passedtherethrough to cool the leading edge.

[0074] An advantage of using the aerofoil of FIGS. 5, 6 or 7 as a wingis that the aircraft can take off and land at lower speed than anaircraft which has a non-variable low profile wing. This reduces thenecessary power for take off. Further, there will be reduced load andwear on tires and undercarriage during landing, as an aircraft utilisingsuch an aerofoil will be able to land at a speed of approximately 100miles per hour (44.7 metres per second) as opposed to one having aconventional non-adjustable low profile wing which may require a landingspeed of 350 miles per hour (156.5 metres per second). Therefore thetires on an aircraft having a preferred variable cross-section aerofoilas a wing will not be required to spin up to such a high speed uponlanding.

[0075] The Coanda blowing slot 14′ shown in the aerofoils of FIGS. 5, 6and 7 may include a plurality of spaced apertures or nozzles, and theapertures or nozzles may include substantially V-shaped notches in theirside walls.

[0076] One preferred arrangement of spaced nozzles is shown in FIG. 8.As can be seen from the plan view in FIG. 8b, the nozzle arrangement isindicated generally by reference numeral 200 and includes a plurality ofspaced nozzles 202 which are spread across a portion of the upperleading panel 15 of the aerofoil and are located underneath the upperleading panel 15. A tube 204 extends from each nozzle 202, the tubes 204converging into a tapering section 206 of the nozzle arrangement. Thetapering section 206 terminates in a tubular portion 208 which may beconnected to a combustion chamber such as that shown schematically inside elevation in FIG. 9. In plan view each nozzle 202 has a convergingregion 210 adjacent the tube 204, a throat 212 adjacent the convergingregion 210, and a diverging outlet portion 214. The maximum includedangle in the diverging outlet portion is about 24° or less. In sideelevation view as shown in FIG. 8c, the shape of the nozzles is similar,although it will be seen that a substantially V-shaped notch is providedin each side wall. It has been found that such nozzle shapes result indesirable characteristics.

[0077] As outlined above, in a preferred embodiment a rocket combustionchamber is provided to blow gas through the nozzle arrangement. Withreference to FIG. 9, a preferred embodiment combustion chamber 18′ isattached to the tubular portion 208 of the nozzle arrangement by athroat section 218. The combustion chamber includes a source 220 ofoxidant which is preferably concentrated hydrogen peroxide with astrength of 80-90% (known as high-test peroxide). The high-test peroxideis pumped through a channel 222 which acts as a cooling jacket andsurrounds the combustion chamber 18, and is delivered through a catalyst224 such as silver-plated nickel gauze into the combustion chamber 18′.The cooling jacket 222 extends into the nozzle arrangement as can beseen from FIGS. 8b and 8 c. This cools the external surface of theaerofoil as the high-test peroxide is passed therethrough. The coolingjacket 222 also serves to transfer heat from within the combustionchamber 18 to the high-test peroxide prior to its entry into thecombustion chamber.

[0078] A pump is provided to pump fuel such as kerosene into thecombustion chamber 18 via a tube 228. The thrust provided by the rocketis variable by changing the amount of fuel pumped into the combustionchamber 18.

[0079] If desired, a plurality of combustion chambers 18 and associatednozzle arrangements may be provided across each aerofoil.

[0080] The flow of heated gas is turbulent at the converging region 210of each nozzle adjacent the tube. The throat 212 determines the rate ofvolume flow of gas through the nozzle. The diverging outlet portion 214of each nozzle allows the gas to expand and provide thrust on thenozzle. The V-shaped notch in each sidewall enables the flow to fan outor disperse in a horizontal plane, to adjoin the flow from neighbouringnozzles, assisting in attachment of the Coanda flow over the aerofoilsurface. As the flow fans out in the horizontal plane, it tapers down inthe vertical plane.

[0081] Rather than providing a single combustion chamber feeding gas toa plurality of nozzles, each nozzle may comprise part of an individualrocket combustion chamber. For example, any number of small rocketcombustion chambers may be provided along the span of the aerofoil toprovide for the same number of Coanda blowing nozzles.

[0082] Such an arrangement is shown in FIGS. 10 and 11. Similarreference numerals are used to indicate similar parts to FIGS. 8 and 9.This embodiment differs in that, rather than providing a separate nozzlearrangement, each nozzle is provided as part of an individual rocketcombustion chamber. The nozzles may again be in the order of 8 mmdiameter.

[0083] Further, rather than including V-shaped notches, the outlets ofthe nozzles are low profile to fan out the exhaust gas.

[0084] Each nozzle includes a converging region 210′ adjacent theinterior of the combustion chamber, and a narrowed throat region 212′. Adiverging region 214′ is again provided adjacent the throat region 212′,but the diverging region 214′ is followed by a further region 215′ whichconverges in the vertical plane. In the horizontal plane the region 215′diverges at an included angle of about 32° or less, to provide a nozzleoutlet which is wider than it is high. This again serves to fan out ordisperse the exhaust gas in the horizontal plane and taper the exhaustgas in the vertical plane. With a number of such combustion chambersprovided side-by-side, the gas from each nozzle 14″ will attach to thegas from the neighbouring nozzle.

[0085] Attachment of the Coanda flow to the wing surface is enhanced byvirtue of the combustion chamber and nozzle 14″ being recessed under theaerofoil surface or leading panel 15, and the aerofoil surface followingthe nozzle 14″ being angled such that the exhaust gas flows directlyonto the surface. It will be appreciated that the exhaust gas will be ata high temperature, and the surface following the nozzle 14″ is curvedto allow for thermal expansion. Further, the channel 222′ again servesto cool the aerofoil surface as the oxidant is passed therethrough.

[0086] While this nozzle arrangement differs from that of FIGS. 8 and 9,it will be appreciated that they both assist in attaching the Coandaflow to the aerofoil surface.

[0087] Test Results

[0088] Test results have shown that providing Coanda blowing slots nearthe upper most position on the aerofoil's front face provided reducednegative lift from the Coanda blowing jet reaction, as well as providingadditional forward thrust, with good entrainment for forward thrust whenreattaching the leading edge breakaway flow.

[0089] The Coanda adhesion effect changes the direction of the Coandablowing, causing it flow around over the aerofoil causing an externalresultant force which creates lift on the aerofoil.

[0090] Tests on an aerofoil of eight foot (2.624 metres) chord lengthand one foot (0.3048 metres) span gave 60 lbs (266.89 Newtons) lift,from a blowing pressure of 300 lbs per square inch (2067 kilopascals)and gave 37 lbs (164.58 Newtons) of forward thrust with no main airflow.

[0091] As the Coanda blowing pressure was increased, lift on theaerofoil was found to increase. This is due to the normal main air flowpassing over the aerofoil being entrained and reattached and thrustdownward together with the flow from the Coanda blowing nozzle. As theCoanda blowing temperature was increased, using a jet engine combustionsystem, the velocity also increased. This resulted in the small increasein forward thrust but no increase in lift. The increased temperaturehowever usefully increased the volume of a given amount of compressedair, thereby increasing the blowing duration from the given amount ofcompressed air by a factor of 2.4.

[0092] The main function of the Coanda blowing nozzles is to reattachthe leading edge breakaway flow by boundary layer control to theaerofoil. The Coanda blowing provides both forward thrust and lift onthe aerofoil, which improves the economics of the aerofoil. Further, theextra Coanda blowing power to the boundary layer control system providesa higher coefficient of lift for the aerofoil. The preferred aerofoil inthe subsonic (higher profile) configuration is a relatively deepaerofoil having a thickness of about 30% of the chord length. WithCoanda blowing it is capable of operating at a high incidence of greaterthan about 22°, giving a high coefficient of lift at landing and takeoffspeed.

[0093] Wind tunnel tests were performed on an aerofoil having a 6″(0.152 metre) chord length and 9″ (0.228 metre) span width, as well asan aerofoil having a 1′ (0.3048 metre) chord length and 9″ (0.228 metre)span width, to provide the following results: Percentage of Percentageof Lift due to Lift due to Main Air Flow Velocity Main Air Flow CoandaEffect 100 ft/sec (30.48 m/sec) 50% 50% 240 ft/sec (73.51 m/sec) 66% 34%350 ft/sec (106.68 m/sec) 75% 25%

[0094] The above results are from compressed air Coanda blowing only, atlimited pressure.

[0095] The coefficient of lift decreased as the main airflow velocityincreased, because the Coanda blowing power remains constant. Largerchord aerofoils enable an increased radius on the curved upper surfaceof the aerofoil which allows for increased Coanda blowing pressure andhence more lift due to the Coanda blowing effect.

[0096] The above describes preferred embodiments of the presentinvention, and modifications may be made thereto without departing fromthe scope of the following claims.

1. An aerofoil which is adjustable between a high profile configurationfor subsonic flow and a low profile configuration for supersonic flowand including a leading edge which generates a subsonic leading edgebreakaway flow in the high profile configuration, an upper surfacehaving a leading portion inclined away from the leading edge, a lowersurface, a trailing edge, and at least one opening provided along theleading portion of the upper surface and arranged to discharge asufficient volume of gas away from the leading edge to assist inreattachment of the leading edge breakaway flow to the upper surface. 2.An aerofoil according to claim 1, wherein the opening is in the form ofa slot.
 3. An aerofoil according to claim 1, wherein the openingscomprise a series of apertures or nozzles spaced along the leadingportion of the upper surface.
 4. (Cancelled)
 5. An aerofoil according toclaim 3 wherein the apertures or nozzles are arranged to disperse thegas over the surface of the aerofoil.
 6. An aerofoil according to claim5, wherein the apertures or nozzles include substantially V-shapedapertures in their side walls.
 7. An aerofoil according to claim 5,wherein the width of the outlet of each nozzle or aperture is greaterthan its height.
 8. An aerofoil according to claim 1, wherein the uppersurface is constituted by a leading surface portion and a trailingsurface portion.
 9. An aerofoil according to claim 8, wherein the upperleading surface portion is constituted by an upper leading panel and theupper trailing surface portion is constituted by an upper trailingpanel.
 10. An aerofoil according to claim 9, wherein the upper trailingpanel is detachably joined to the remainder of the upper surface tofacilitate movement between the high profile configuration and the lowprofile configuration.
 11. An aerofoil according to claim 10, whereinthe detachable joint is in the form of a sliding lap joint.
 12. Anaerofoil according to claim 11, wherein the sliding lap joint includes aroller rotatably mounted to the upper trailing panel which is slidablein a curved channel extending from the upper leading panel.
 13. Anaerofoil according to claim 1, wherein the lower surface is defined by aleading panel, a central panel, and a trailing panel.
 14. An aerofoilaccording to claim 13, wherein the lower leading panel and the lowertrailing panel are hingedly connected to the lower central panel.
 15. Anaerofoil according to claim 13 of 14, wherein the lower central panelincludes a transverse bend which defines a lower central panel leadingportion and a lower central panel trailing portion.
 16. An aerofoilaccording to claim 13, and including an upper leading panel, wherein theupper leading panel is fixedly attached to the lower leading panel atthe leading edge.
 17. An aerofoil according to claim 13, and includingan upper trailing panel, wherein the upper trailing panel is fixedlyattached to the lower trailing panel at the trailing edge.
 18. Anaerofoil according to claim 13, wherein the lengths of the lower leadingpanel and the lower trailing panel are significantly less than thelength of the lower central panel.
 19. An aerofoil according to claim 1,wherein the aerofoil includes two internal hydraulic jacks to facilitateadjustment between the low profile configuration and the high profileconfiguration.
 20. An aerofoil according to claim 1, including two mainstructural support beams extending longitudinally of the aerofoil. 21.(Cancelled)
 22. An aerofoil according to claim 1, wherein the leadingedge is rounded.
 23. An aerofoil according to claim 22, wherein therounded leading edge includes a section through which cooling fluid orgas may pass to cool the leading edge.
 24. (Cancelled)
 25. An aerofoilaccording to claim 22, wherein the portion of the aerofoil adjacent toand including the leading edge includes a high temperature resistantlayer.
 26. An aerofoil according to claim 25, wherein the hightemperature resistant layer comprises a ceramic material.
 27. Anaerofoil according to claim 1, including means to heat the gas.
 28. Anaerofoil according to claim 27, wherein the means to heat the gascomprises a combustion chamber within the aerofoil.
 29. An aerofoilaccording to claim 28, wherein the means to heat the gas is a rocketchamber provided within the aerofoil which is arranged to exhaust heatedgas to the opening(s).
 30. An aerofoil according to claim 29, whereinthe openings comprise a plurality of nozzles, and an arrangement isprovided to exhaust heated gas from the rocket chamber to at least someof the plurality of nozzles.
 31. An aerofoil according to claim 29,including one or more rocket chambers, with each opening comprising partof a respective rocket chamber.
 32. An aerofoil according to claim 27,including means to heat the gas adjacent to but in operable connectionwith, the aerofoil.
 33. An aerofoil according to claim 1, wherein atleast one further opening is provided along a region of the uppersurface between the opening(s) along the leading portion of the uppersurface and the trailing edge, to discharge gas towards the trailingedge and further assist the attachment of airflow over the uppersurface.
 34. An aerofoil according to claim 33, wherein the furtheropening is in the form of a slot.
 35. An aerofoil according to claim 33,wherein the further openings comprise a plurality of apertures ornozzles arranged along the trailing surface portion of the uppersurface.
 36. (Cancelled)
 37. An aerofoil according to claim 35, whereinthe apertures or nozzles in the trailing surface portion are arranged todisperse the gas over the trailing surface portion of the aerofoil. 38.An aerofoil according to claim 37, wherein the apertures or nozzles inthe trailing surface portion include substantially V-shaped apertures intheir side walls.
 39. An aerofoil according to claim 37, wherein thewidth of the outlet of each aperture or nozzle in the trailing surfaceportion is greater than its height.
 40. An aerofoil according to claim1, wherein the aerofoil is a wing.
 41. An aerofoil according to claim40, which is movably attached to an aircraft such that its angle ofincidence to oncoming airflow is selectively variable.
 42. An aerofoilaccording to claim 1, wherein the depth of the aerofoil in the highprofile configuration is about 30% of the chord length of the aerofoil.43. An aerofoil according to claim 1, wherein at least a substantialpart of the upper and lower surfaces move relative to one another whenthe aerofoil is adjusted between the high profile and low profileconfiguration.